Environment-compliant image display system and program

ABSTRACT

To provide an environment-compliant image display system and program, there is provided a color control processing update section which corrects colors by adjusting a LUT in a 3D-LUT storage section and corrects brightness by adjusting γ values in a 1D-LUT storage section, to increase an output value in at least a lower grayscale range when the environment is affected by ambient light, based on environmental information that has been obtained by a colored-light sensor.

[0001] Japanese Patent Application No. 2000-230949, filed Jul. 31, 2000,is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an environment-compliant imagedisplay system and program.

[0004] 2. Description of Related Art

[0005] When displaying images at a plurality of different locations (inpresentations, meetings, medical treatments, the design and fashionfield, business activities, education, as well as general-purpose imagessuch as those in movies, TV, video, and games), an important part ofachieving effective presentations is to make it possible to reproduceimages exactly as the creator of those images intended, whatever thelocation.

[0006] One way of considering how to adjust the viewing of such imagesis management of the input-output characteristics of the device toachieve color management in the reproduction of colors. Specific methodsof how to achieve this are not, however, clear.

[0007] When projecting and displaying an image with a projector andscreen, in particular, it is difficult to reproduce colors in a suitablemanner without considering not only ambient light but also the screentype.

[0008] Recent advances in increasing resolution of projectors have madecolor reproducibility important as well.

[0009] Particularly if the environment is affected by ambient light suchas artificial light, a state can occur in which the chroma values of thecolors are adversely affected by the brightness, making it impossible toreproduce colors appropriately.

SUMMARY OF THE INVENTION

[0010] The present invention was devised in the light of theabove-described technical problem and has as an objective thereof theprovision of an environment-compliant image display system and programthat make it possible to reproduce suitable colors, even in anenvironment that is affected by ambient light.

[0011] (1) In order to solve the above described technical problem,according to one aspect of the present invention, there is provided anenvironment-compliant image display system which corrects an image,based on environmental information that expresses visual environment inan area in which the image is displayed, and displays the image; theimage display system comprising:

[0012] correction means which corrects input-output characteristic datafor display that is used by a means for displaying the image, thecorrection being in such a manner as to increase an output value in atleast a lower grayscale range when the environment is affected byambient light, based on the environmental information.

[0013] (2) According to another aspect of the present invention, thereis provided an environment-compliant image display system which correctsan image, based on environmental information that expresses visualenvironment in an area in which the image is displayed, and displays theimage; the image display system comprising:

[0014] a correction section which corrects input-output characteristicdata for display that is used by a means for displaying the image, thecorrection being in such a manner as to increase an output value in atleast a lower grayscale range when the environment is affected byambient light, based on the environmental information.

[0015] (3) According to further aspect of the present invention, thereis provided a program embodied on an information storage medium or in acarrier wave, the program for correcting an image, based onenvironmental information that expresses visual environment in an areain which the image is displayed, and displaying the image; the programimplementing in a computer:

[0016] correction means for correcting input-output characteristic datafor display that is used by a means for displaying the image, thecorrection being in such a manner as to increase an output value in atleast a lower grayscale range when the environment is affected byambient light, based on the environmental information.

[0017] These aspects of the present invention make it possible to reducethe deterioration of chroma and thus achieve suitable colorreproduction, by increasing an output value in a lower grayscale rangeif the chroma of the image is adversely affected by ambient light.

[0018] An output value in lower grayscale range is particularly prone todeterioration in comparison with that of higher grayscale range, inother words, they are readily affected by ambient light. These aspectsof the invention make it possible to reduce the effects of ambient lightand achieve suitable color reproduction even if the environment isadversely affected by ambient light.

[0019] Note that the correction means of this image display system orprogram could also correct the input-output characteristic data fordisplay that is used by a means for displaying the image, in such amanner that an output value within entire grayscale range is increased.

[0020] Note that “visual environment” in this case refers to factorssuch as ambient light (artificial light, natural light, etc.) and theobject on which the image is displayed (display device, wall surface,screen, etc.).

[0021] This environmental information could be values that express colorand brightness, such as xyY, or color and brightness correction amounts,such as ΔxΔyΔy.

[0022] When implementing such an image display system, it is possible todo so by using means such as a projector or monitor.

[0023] (4) In this image display system and program, the correctionmeans may correct the input-output characteristic data by performing apredetermined calculation using parameters that differ between a lowergrayscale range and a grayscale range other than the lower grayscalerange.

[0024] This makes it possible to achieve a suitable output value inaccordance with a gray level by using different parameters for a lowergrayscale range and a grayscale range other than the lower grayscalerange.

[0025] In other words, an output value in a higher grayscale range wouldbe increased too far if the same equation as used for increasing anoutput value in the lower grayscale range is used, and it could happenthat the image will break up.

[0026] Excessive increasing of the output value can be prevented byusing parameters that differ between a lower grayscale range and agrayscale range other than the lower grayscale range in accordance withthe present invention, thus making it possible to reduce the likelihoodof a situation such as one in which the image breaks up.

[0027] (5) In this image display system and program, the correctionmeans may correct the input-output characteristic data by performing apredetermined calculation based on a difference between a brightnessvalue for actual environment which is comprised within the environmentalinformation, and a brightness value for an ideal environment.

[0028] This makes it possible to easily determine how much correction toapply to the input-output characteristic data, from the differencebetween the brightness value of the actual environment and thebrightness value of an ideal environment (such as ΔY). This ensures thatthe amount of correction of the input-output characteristic data can beobtained rapidly.

[0029] Note that the actual environment in this case refers to theenvironment in which the image display system is used in practice, whichis affected by external factors such as ambient light, and the idealenvironment is hypothetical usage environment that is determinedbeforehand. The brightness value refers to a value that expressesbrightness in units such as candela per square meter (cd/m²) or lux(lx).

[0030] (6) In this image display system and program, the correctionmeans may perform gamma correction as at least part of the correction ofthe input-output characteristic data.

[0031] This makes it possible to increase an output value in a lowergrayscale range by lowering the gamma value, when an output value in thelower grayscale range has deteriorated because of the effects of ambientlight, by way of example. This enables reduction of the effects ofambient light and suitable color reproduction, even when the environmentis adversely affected by ambient light.

[0032] Note that if the gamma correction amount is Δγ in this case, theequation that is used for these calculations during gamma correctioncould be: Δγ=−hα(γ−γmin)/(1+|hα|).

[0033] In this case, h is an adjustment parameter (or it could be aconstant), α is the environmental information for brightness correctionobtained by the visual environment detection means, and γmin is theminimum value of γ used as data for conversion control. This γmin isused for adjusting the values of the above equation so as to lie withina suitable range.

[0034] This makes it possible to correct the image automatically inaccordance with the visual environment, by determining the visualenvironment and correcting the image continuously.

[0035] (7) In this image display system and program, the correctionmeans may correct color modification information that is stored in apredetermined storing region, in such a manner that a color temperatureof the image to be displayed is adjusted, based on a brightness valuefor the actual environment that is comprised within the environmentalinformation.

[0036] This makes it possible to reproduce the colors of the imagesuitably, by adjusting the color temperatures in accordance with thebrightness of external factors such as the ambient light in practice.

[0037] (8) In this image display system and program, the colormodification information may be a three-dimensional look-up table.

[0038] In them prior art, a one-dimensional look-up table (1D-LUT) isused with the objective of providing refinements such as colortemperature adjustment, γ correction, and correction of thecharacteristics of the display elements.

[0039] To achieve high-quality color management, however, it isnecessary to aim for consistency of reproducible color gamuts betweenother display devices having different reproducible color gamuts and astandard color space (sRGB, for example).

[0040] It is also necessary to match the reproducible color gamut of adisplay device that has been affected by its environment with thereproducible color gamut of other display devices or the standard colorspace. To achieve such matching of the reproducible color gamut,corrections called color compression and color expansion are applied.

[0041] When it comes to matching two reproducible color gamuts, someparts of one reproducible color gamut will project from the otherreproducible color gamut, and other parts of the first reproduciblecolor gamut will be within the other reproducible color gamut. For thatreason, it is necessary to perform corrections that apply compression toareas of a specific color or expansion to areas of another specificcolor, within the same reproducible color gamut.

[0042] It is difficult to implement such color control over specificareas by using 1D-LUTs to control the gamma values of each RGB color.Even though a 1D-LUT is a mapping table, it can only control primarycolors and it is difficult to apply different levels of control for eachcolor. On the other hand, a three-dimensional look-up table (3D-LUT)makes it possible to control each color, even if they are not primarycolors, which enables variable control (color compression and colorexpansion) for each area of color such as those described above.

[0043] The use of a 3D-LUT as color modification information makes itpossible to control features such as variable color compression andcolor expansion for each area of color, which is difficult with a1D-LUT, thus enabling accurate color reproduction.

[0044] The correction means could correct a gamma table that is at leastpart of the one-dimensional look-up table, as the gamma correction.

[0045] The image display system may comprise visual environmentdetection means for measuring at least one of the color value, gamma,and color temperature of an image that is displayed in the image displayarea.

[0046] Similarly, the environmental information in the program may beinformation from a visual environment detection means for measuring atleast one of the color value, gamma, and color temperature of an imagethat is displayed in the image display area.

[0047] In this case, “color values” refers to indices that expresscolors by factors such as tri-stimulus values, chromaticity coordinates,spectrum distribution, excitation purity, or main wavelength.

[0048] Note that this visual environment detection means could be one ora combination of several different devices, such as a luminance sensorthat measures the luminance value of the image display area, acolored-light sensor that measures the RGB values or XYZ values of theimage display area, or a chromaticity sensor that measures thechromaticity values of the image display area.

[0049] In this image display system and program, the image display areacould be an area on a screen.

[0050] This image display system can be applied in a satisfactory mannereven when the way in which colors are seen is greatly changed bymaterials such as the screen.

[0051] This image display system may also comprise:

[0052] means for displaying an image that prompts the input of the typeof the screen; and

[0053] means for inputting the thus-input type of the screen as at leastpart of the environmental information.

[0054] This program may implement in a computer:

[0055] means for causing a display means to display an image thatprompts the input of the type of the screen; and

[0056] means for causing an input means to input the thus-input type ofthe screen as at least part of the environmental information.

[0057] This makes it possible to correct the colors and brightness of animage in a suitable manner, by determining the visual environment of thescreen in a manner that cannot be considered in the prior art.

[0058] In particular, since there is only a small number of screen typesand people can easily distinguish between them, there is littlelikelihood of a decision error during input of this screen type and thusit is possible to determine the screen type accurately.

[0059] Note that this screen could be of a reflective type or atransmission type.

[0060] In this image display system and program, the visual environmentdetection means may determine the visual environment with reference tothe screen type.

[0061] This visual environment detection means could comprise a sensorthat determines the screen characteristics, by way of example.

[0062] More specifically, the screen characteristics could be determinedby using a sensor such as a colored-light sensor to measure reflectedlight (or transmitted light) when a white light is projected.

[0063] This makes it possible to determine the visual environment inlight of the screen type, and also absorb differences in screen type byapplying correction such as gamma correction or color temperaturecorrection that is based on the result of this determination. It is thuspossible to reproduce substantially the same colors, irrespective of thescreen type.

[0064] With PCs or the like that use operating systems with internalprior-art color management systems, in particular, the onlyconsideration is the type of display connected to the PC. In addition,methods of performing color correction from consideration of ambientlight have been proposed, but there is nothing that considers the typeof the screen that forms the area in which the image is displayed.

[0065] The present invention makes it possible to create and displayimages that reflect the visual environment in a suitable manner, byapplying color correction after determining the visual environment withreference to the screen type.

[0066] In this image display system, the visual environment detectionmeans may also comprise means for determining the visual environment bymeasuring at least ambient light.

[0067] Similarly, in the program, the visual environment detection meansmay determine the visual environment by measuring at least ambientlight.

[0068] This makes it possible to determine the visual environment by amethod such as measuring the ambient light. Ambient light within thevisual environment has a huge effect on the way in which an image isseen. The visual environment can be determined in a suitable manner bymeasuring the ambient light which is a major factor in how an image isseen.

BRIEF DESCRIPTION OF THE DRAWINGS

[0069]FIG. 1 is a schematic illustrative view of a presentation systemthat uses a laser pointer in accordance with an example of thisembodiment of the present invention;

[0070]FIG. 2 is a functional block diagram of the image processingsection within a prior-art projector;

[0071]FIG. 3 is a functional block diagram of the image processingsection within a projector in accordance with an example of thisembodiment of the present invention;

[0072]FIG. 4 is a functional block diagram of the image processingsection within a projector in accordance with another example of thisembodiment of the invention;

[0073]FIG. 5 shows the variation of Δγ with respect to α in accordancewith an example of this embodiment of the invention;

[0074]FIG. 6 shows the variation of γ′ with respect to α in accordancewith an example of this embodiment of the invention;

[0075]FIG. 7 shows variations in an output value with respect to themodified grayscale x after γ correction;

[0076]FIG. 8 shows variations in an output value when the values of γ′are made to be different for a lower grayscale range and a grayscalerange other than the lower grayscale range, in accordance with anexample of this embodiment of the invention;

[0077]FIG. 9 shows variations in output for a lower grayscale range andvariations in output for a grayscale range other than a lower grayscalerange, in accordance with an example of this embodiment of theinvention;

[0078]FIG. 10 shows variations in WRGB chromaticity when gray level isvaried, expressed as an xy chromaticity diagram where the illuminance isapproximately 600 lx and the γ value of the projected image is 2.0;

[0079]FIG. 11 shows variations in WRGB chromaticity when gray level isvaried, expressed as an xy chromaticity diagram where the illuminance isapproximately 600 lx and the γ value of the projected image is 1.0;

[0080]FIG. 12 shows variations in WRGB chromaticity when gray level isvaried, expressed as an xy chromaticity diagram where the illuminance isapproximately 600 lx and the γ value of the projected image is 0.5;

[0081]FIG. 13 shows variations in WRGB chromaticity when gray level isvaried, expressed as an xy chromaticity diagram where the illuminance isapproximately 300 lx and the γ value of the projected image is 2.0;

[0082]FIG. 14 shows variations in WRGB chromaticity when gray level isvaried, expressed as an xy chromaticity diagram where the illuminance isapproximately 300 lx and the γ value of the projected image is 1.0;

[0083]FIG. 15 shows variations in WRGB chromaticity when gray level isvaried, expressed as an xy chromaticity diagram where the illuminance isapproximately 300 lx and the γ value of the projected image is 0.5;

[0084]FIG. 16 shows variations in color temperature when gray level isvaried, where the illuminance is approximately 600 lx and the γ value ofthe projected image is 2.0, 1.0, and 0.5; and

[0085]FIG. 17 shows variations in color temperature when gray level isvaried, where the illuminance is approximately 300 lx and the γ value ofthe projected image is 2.0, 1.0, and 0.5.

DETAILED DESCRIPTION OF THE EMBODIMENT

[0086] The description below relates to a case in which the presentinvention is applied to an image display system which uses aliquid-crystal projector and which can adapt to the environment, by wayof example, with reference to the accompanying figures.

[0087] Description of Overall System

[0088] A schematic illustrative view shown in FIG. 1 is of apresentation system that makes use of a laser pointer 50, in accordancewith an example of this embodiment of the present invention.

[0089] A projector 20 that is provided substantially facing a screen 10projects an image for a predetermined presentation. A presenter 30 givesa presentation to an audience, while using a light spot 70 projectedfrom the laser pointer 50 to point at a desired position of an image inan image display region 12, which is an image display area on thescreen.

[0090] During such a presentation, the way in which images on the imagedisplay region 12 are seen will vary greatly, depending on factors suchas the type of the screen 10 and ambient light 80. When the samewhite isdisplayed, for example, it could seem to be white with a yellow cast orwhite with a blue cast, depending on the type of the screen 10. Evenwhen the same white is displayed, it could seem to be a bright white ora dull white if the ambient light 80 differs.

[0091] Recently, the projector 20 has become smaller and easy totransport. For that reason, it has become possible to performpresentations at a client's location, by way of example, but it isdifficult to adjust colors to match the environment at the client'slocation and the manual adjustment of colors at the client's locationtakes too much time.

[0092] A functional block diagram of the image processing section withina prior-art projector is shown in FIG. 2.

[0093] This prior-art projector inputs an R1 signal, a G1 signal, and aB1 signal (which for RGB signals in analog format, sent from a PC or thelike) to an A/D converter section 110, and uses a projector imageprocessing section 100 to perform color modification on an R2 signal, aG2 signal, and a B2 signal which have been converted into digital formby the A/D converter section 110.

[0094] A D/A converter section 180 converts an R3 signal, a G3 signal,and a B3 signal, which have been subjected to the color modification ofthe projector image processing section 100, into analog form and outputsthem as an R4 signal, a G4 signal, and a B4 signal. A light valve (L/V)drive section 190 drives liquid-crystal light bulbs to display an image,based on the R4 signal G4 signal, and B4 signal.

[0095] The projector image processing section 100, which is controlledby a CPU 200, comprises a projector color conversion section 120 and aprofile management section 130.

[0096] The projector color conversion section 120 converts the RGBdigital signals (the R2 signal, G2 signal, and B2 signal) into RGBdigital signals for projector output (the R3 signal, G3 signal, and B3signal), based on a projector input-output profile that is managed bythe profile management section 130. Note that “profile” in this caserefers to characteristic data.

[0097] In this manner, the prior-art projector can only perform colormodification based on an input-output profile that indicatesinput-output characteristics that are specific to that particularprojector, so no consideration is paid to the visual environment inwhich the image is projected and displayed.

[0098] However, it is difficult to make the way in which colors are seenuniform in this manner, without taking the visual environment intoaccount. The way in which colors are seen is determined by threefactors: light, the reflection or transmission of light by objects, andvision.

[0099] This embodiment of the present invention implements an imagedisplay system that can reproduce an image with the same visualappearance, by determining the visual environment of light and thereflection or transmission of light by objects, irrespective of theenvironment in which it is applied.

[0100] More specifically, the device is provided with a colored-lightsensor 417 that functions as visual environment detection means fordetermining the visual environment, as shown in FIG. 1, andenvironmental information from the colored-light sensor 417 is input tothe projector 20. To be more specific, the colored-light sensor 417measures colored-light information (more specifically, informationindicating xyY colors and brightness) of the image display region 12within the screen 10.

[0101] The projector 20 is provided with color control processing meanshaving a storage area for storing color correction information andbrightness correction information that is one type of input-outputcharacteristic data for display that is used by a means for displayingan image, and correction means for correcting the color correctioninformation and brightness correction information, based onenvironmental information from the colored-light sensor 417.

[0102] The description now turns to the function blocks of the imageprocessing section of the projector 20, which comprises this colorcontrol processing means and this correction means.

[0103] A functional block diagram of the image processing section withinthe projector 20 in accordance with an example of this embodiment of theinvention is shown in FIG. 3.

[0104] The image processing section comprises an input signal processingsection 401 to which RGB signals are input, a color control processingsection 420, a calibration section 430 that functions as correctionmeans, an output signal processing section 405, and an L/V drive section406.

[0105] The input signal processing section 401 comprises an A/Dconverter section 440 that converts the R1, G1, and B1 analog imagesignals into the R2, G2, and B2 digital image signals.

[0106] The color control processing section 420 comprises athree-dimensional look-up table (3D-LUT) storage section 403 that isused in correcting the color information and a 1D-LUT storage section404 that is used in correcting the brightness information.

[0107] Note that a gamma table and color balance table (or just one ofthem) are stored as part of the brightness correction information in the1D-LUT storage section 404. Similarly, a color-gamut correction tableand a color temperature correction table (or just one of them) arestored as part of the color correction information in the 3D-LUT storagesection 403.

[0108] With a prior-art projector, color control is done with a 1D-LUTand brightness correction is done by determining what potential is usedwhen sampling the input signal.

[0109] During the correction of the brightness of colors to bereproduced, it is necessary to increase an output value in a lowergrayscale range. In this case, the projector 20 of this embodiment ofthe present invention performs brightness correction by using a 1D-LUTthat can manipulate a grayscale characteristic.

[0110] As previously described, the projector 20 of this embodiment ofthe invention performs color correction by using a 3D-LUT, to ensureappropriate color compression or color expansion for each color when itcomes to matching other reproducible color gamuts by color control.

[0111] In this manner, brightness and color can be corrected separately,based on environmental information relating to brightness andenvironmental information relating to color, making it possible toperform each type of correction more precisely.

[0112] With this embodiment of the present invention, the values of agamma correction table within the 1D-LUT storage section 404 arecorrected to increase the output for the entire grayscale range when theenvironment is affected by ambient light, to suppress deterioration ofthe chroma values of the colors. This makes it possible to reproducecolors in substantially the same manner as that when the environment isnot affected by ambient light. Since a lower grayscale range isparticularly likely to be affected by ambient light, in comparison witha higher grayscale range, it is possible to reproduce colors insubstantially the same manner as that when the environment is notaffected by ambient light, by performing γ correction in such a manneras to increase an output value in at least the lower grayscale range.

[0113] The description now turns to color correction, which will befollowed by a description of brightness correction.

[0114] Color Correction

[0115] The calibration section 430 comprises a calibration imagepresentation section 407 which inputs image signals for calibration(correction) to the input signal processing section 401, a colorconversion section 408 which converts colors for conversion (stored inthe 3D-LUT storage section 403) from the RGB color system into the XYZcolor system, and a color control processing update section 460 whichperforms color and brightness correction, based on environmentalinformation that is input from the colored-light sensor 417.

[0116] Note that the RGB system results in device-dependent colors thatvary with the input-output device, such as a projector, but the XYZsystem results in non-device-dependent colors.

[0117] The color conversion section 408 takes the color information thatis stored in RGB format (Ri, Gj, and Bk, where i, j, and k are integersin this document) in the 3D-LUT storage section 403 and converts it intocolor information (Xi, Yj, Zk) . In other words, the color informationis managed in a plurality of grayscales.

[0118] The color conversion section 408 temporarily stores that colorinformation (Xi, Yj, Zk) in a 3D-LUT storage section 409 and outputs itto the color control processing update section 460.

[0119] The color control processing update section 460 converts thecolor information (Xi, Yj, Zk) stored in the 3D-LUT storage section 409,based on environmental information from the colored-light sensor 417.

[0120] The colored-light sensor 417 functions as a visual environmentdetection means that determines the visual environment. Thecolored-light sensor 417 could be one or a combination of severaldifferent devices, such as a luminance sensor that measures theluminance value of the image display area, a colored-light sensor thatmeasures the RGB values or XYZ values of the image display area, or achromaticity sensor that measures the chromaticity values of the imagedisplay area.

[0121] This environmental information is environmental information forcolor correction and environmental information for brightnesscorrection.

[0122] In this case, the environmental information for color correctioncould be information such as white-light chromaticity of theillumination, chromaticity correction request information (such as acolor difference or chromaticity difference), color phase, colortemperature change request information, or the correlated colortemperature of the illumination, by way of example.

[0123] Similarly, the environmental information for brightnesscorrection could be brightness (luminance) of the illumination, imagesignal brightness correction request information (such as ΔY), imageoutput adjustment information, image contrast, or contrast correctionrequest information, by way of example.

[0124] Note that information that combines environmental information forcolor correction and environmental information for brightness correction(in a form such as xyY) could also be used as the environmentalinformation.

[0125] The calibration section 430 comprises a target color temperaturemanagement section 472 for managing the color temperature of thereproduced image.

[0126] The target color temperature management section 472 outputs colortemperature information (T) to the color control processing updatesection 460. More specifically, the color temperature information (T) inthis case is information such as a target color temperature, a targetcorrelated color temperature, the chromaticity of the target colortemperature, or the chromaticity of the target correlated colortemperature.

[0127] If there are adverse effects such as those of artificial light,it is difficult to accurately reproduce a color temperature to act as atarget, such as a target color temperature. In this case, the colorcontrol processing update section 460 obtains the color information(X′i, Y′j, Z′k), based on the environmental information, in such amanner that an image of the color temperature T can be reproduced in astate that is affected by factors such as the artificial light inpractice, by outputting an image so as to form the color temperature T′from consideration of effects such as those of artificial light.

[0128] The color control processing update section 460 outputs thethus-obtained tri-stimulus values (X′1, Y′1, Z′1) to a post-correction3D-LUT storage section 414.

[0129] The color conversion section 408 converts the (X′1, Y′1, Z′1)values in the post-correction 3D-LUT storage section 414 into (R′1, G′1,B′1) values, then outputs the converted (R′1, G′1, B′1) values to the3D-LUT storage section 403.

[0130] In this manner, it is possible to reproduce colors to suit thevisual environment, by overwriting the colors of the 3D-LUT in the3D-LUT storage section 403, based on the visual environment.

[0131] In this manner, it is possible to reproduce colors to suit thevisual environment, by overwriting the colors of the 3D-LUT in the3D-LUT storage section 403, based on the visual environment.

[0132] Brightness Correction

[0133] The description now turns to brightness correction.

[0134] This brightness correction is done by the color controlprocessing update section 460 correcting the γ values in the 1D-LUTstored in 1D-LUT storage section 404.

[0135] More specifically, the color control processing update section460 uses the following equations to obtain the amount of correction Δγfor γ and γ′ after correction:

Δγ=−hα(γ−γmin)/(1+|hα|)

γ′=γ+Δγ

[0136] Note that in this case, h is an adjustment parameter (or it couldbe a constant), α is the previously described environmental informationfor brightness correction, and γ min is the minimum value of γ used asdata for conversion control.

[0137] This γmin is used for adjusting the values of the above equationsso as to lie within a suitable range.

[0138] The description now turns to a specific example of obtaining Δγ.

[0139] The variation in Δγ with respect to α in accordance with thisexample of the present invention is shown in FIG. 5. Similarly, thevariation in γ′ with respect to α in accordance with this example of thepresent invention is shown in FIG. 6.

[0140] In this case, the description concerns a default γ of 1.8, γminis 0.3, and h is 0.1.

[0141] It is assumed in this case that when the value of theenvironmental information for brightness correction α is 10, in otherwords, when the brightness is greater than that of the visualenvironment, the value of Δγ is −0.75 and the value of γ′ is 1.05. Thatis to say, when the visual environment is bright because of the effectsof artificial light or the like, the value of γ falls.

[0142] If the value of the environmental information for brightnesscorrection α is −10, in other words, if it is darker than the standardvisual environment the value of Δγ is 0.75 and the value of γ′ is 2.55.That is to say, when the visual environment is dark because of theeffects or artificial light or the like, the value of γ rises.

[0143] The variation of the output with respect to the modifiedgrayscale x after γ correction is shown in FIG. 7.

[0144]FIG. 7 shows the variation in output of white light (W) when thevalue of α 10 is 10, with the conditions shown in FIGS. 5 and 6.

[0145] As can be seen from FIG. 7, an output value in a lower grayscalerange (such as 0.00 to 0.20) is relatively large in comparison withoutputs in medium and higher grayscale ranges (such as 0.30 to 1.00).

[0146] This makes it possible to depict an image in which output isgreater in the lower grayscale range, making it possible to reduce theeffects of artificial light which affects the lower grayscale range inparticular.

[0147] Note that the situation is similar for the RGB primary colorsignals; not just for white light (W).

[0148] The effects of artificial light in the lower grayscale range canbe corrected if the γ value is small, but if the output in the highergrayscale range is too high, the contrast is reduced and thus it canhappen that the image will appear to break up.

[0149] If the γ′ values for a lower grayscale range and a grayscalerange other than a lower grayscale range are made different in such acase, the projector 20 will be able to reproduce colors suitably in thelower grayscale range as well as in the grayscale range other than thelower grayscale range.

[0150] The graph of FIG. 8 shows variations in output when the values ofγ′ are made to be different for a lower grayscale range and a grayscalerange other than a lower grayscale range, in accordance with an exampleof this embodiment of the invention. Similarly, the graph of FIG. 9shows variations in output for a lower grayscale range and variations inoutput for a grayscale range other than a lower grayscale range, inaccordance with an example of this embodiment of the invention.

[0151] The output for the lower grayscale range is obtained fromY1=Wmax1*x^ γ1′ and the output for the grayscale range other than thelower grayscale range is obtained by Y2=Wmax2*x^ γ2′, as shown by way ofexample in FIG. 9. Note that the “^ ” symbol in this case means “raiseto the power of”.

[0152] In this graph, γ1′ is the γ value after correction for the lowergrayscale range and γ2′ is the γ value after correction for thegrayscale range other than the lower grayscale range. As can be seenfrom FIG. 9, the values are set as described below to ensure that Y1 isgreater than Y2 in the lower grayscale range but less than Y2 in thehigher grayscale range.

[0153] Assume that γmin1 for the lower grayscale range is 0.3 and γmin2for the grayscale range other than the lower grayscale range is 1.2, byway of example, and the other values are α=10, h=1, and the defaultγ=1.8, in the same manner as described previously.

[0154] In such a case, calculations are performed using the equation forobtaining γ′, as described previously, to obtain:

γ′1 (for the lower grayscale range)=0.44

γ′2 (for the grayscale range other than the lower grayscale range)=1.25

[0155] The graph of Y1 and Y2 shown in FIG. 9 can be drawn by settingthe values Wmax1=0.5 and Wmax2=1.0, by way of example.

[0156] The graph of FIG. 8 can be drawn by using Y1 for lower grayscalerange and Y2 for grayscale range other than the lower grayscale range.

[0157] In this manner, the projector 20 can reduce break-up of the imagein the higher grayscale range and thus reproduce a more suitable image,by adjusting the parameters for the lower grayscale range and thegrayscale range other than the lower grayscale range.

[0158] The color control processing update section 460 updates the γvalues of the 1D-LUT stored in the 1D-LUT storage section 404 with thethus-obtained γ′ values.

[0159] This ensures that the projector 20 can reproduce brightness in amanner that is suitable for the visual environment, by overwriting the1D-LUT of the 1D-LUT storage section 404, based on the visualenvironment.

[0160] The color control processing section 420 outputs to the outputsignal processing section 405 the image signals (R3, G3, and B3) thathave been adjusted using the look-up tables (LUTs) in the 1D-LUT storagesection 404 for brightness correction and the 3D-LUT storage section 403for color correction.

[0161] The output signal processing section 405 uses a D/A convertersection 441 to convert the digital image signals (R5, G5, and B5) intoanalog image signals (R6, G6, and B6), then outputs the converted analogimage signals to the L/V drive section 406.

[0162] The L/V drive section 406 uses those analog image signals todrive liquid-crystal light bulbs to regulate the image projected fromthe projector 20.

[0163] In this above described manner, the way in which the image isseen in the image display region 12 of the screen 10 can be adjusted asappropriate by adjusting the image projected by the projector 20.

[0164] This embodiment of the present invention therefore ensures thatthe visual environment is considered when an image is projected anddisplayed.

[0165] This makes it possible to absorb differences between displayenvironments and thus display the same image regardless of theenvironment to which it is applied. It is therefore possible toreproduce substantially the same colors in a plurality of differentlocations, within a short time.

[0166] With color and brightness correction that reflects the effects ofthe visual environment, the visual environment is continuouslydetermined by the colored-light sensor 417 and the corrected colorinformation and γ values are continuously obtained by the color controlprocessing update section 460. This embodiment of the present inventiontherefore makes it possible for the projector 20 to correct the imageautomatically from consideration of the visual environment.

[0167] This makes it possible to adjust the image accurately within ashorter time than that required when the way in which the image is seenis adjusted manually.

[0168] The projector 20 can also increase an output value in lowergrayscale range and correct the brightness of the reproduced colors byusing a 1D-LUT that enables manipulation of the grayscale characteristicduring the brightness correction.

[0169] The projector 20 can also apply color compression and colorexpansion independently for each color, by using a 3D-LUT for the colorcorrection.

[0170] In this manner, it is possible to apply brightness correction andcolor correction separately, based on environmental information relatingto brightness and environmental information relating to color, thusenabling it to apply both types of correction more precisely.

[0171] Specific Discussion of Effects

[0172] The description now turns to specific details of the effects ofbrightness and color correction, using experimental results obtained bythe present inventors.

[0173] The graph of FIG. 10 shows variations in WRGB chromaticity whengray level is varied, expressed as an xy chromaticity diagram where theilluminance is approximately 600 lux (lx) and the γ value of theprojected image is 2.0, the graph of FIG. 11 shows those variations whenthe illuminance is approximately 600 lx and the γ value of the projectedimage is 1.0, and the graph of FIG. 12 shows those variations when theilluminance is approximately 600 lx and the γ value of the projectedimage is 0.5.

[0174] Similarly, the graph of FIG. 13 shows variations in WRGBchromaticity when gray level is varied, expressed as an xy chromaticitydiagram where the illuminance is approximately 400 lx and the γ value ofthe projected image is 2.0, the graph of FIG. 14 shows those variationswhen the illuminance is approximately 300 lx and the γ value of theprojected image is 1.0, and the graph of FIG. 15 shows those variationswhen the illuminance is approximately 300 lx and the Y value of theprojected image is 0.5.

[0175] The WRGB chromaticity is positioned further outward as the graylevel increases and approaches a point as the gray level decreases. Thelocation of the point of approach is a white or gray area in the xychromaticity diagram where the excitation purity (chroma) is low.

[0176] Under illumination, the projection light of the projector 20 andthe artificial light are subjected to additive color mixing so that theexcitation purity (chroma) of an image under illumination willdeteriorate. The lower grayscale range of the image in particular have alow luminance from the projection light, so they are readily affected bythe illumination and the chroma deterioration is likely to be large.

[0177] As can be seen from FIGS. 10 to 15, there is an effect by whichthe deterioration of the lower grayscale excitation purity (chroma) canbe suppressed by reducing the γ value even under illumination.

[0178] With the 300-lx illumination of FIGS. 13 to 15, the effect isincreased with smaller values of γ value, in comparison with the 600-lxillumination of FIGS. 10 to 12. This is because the effect of artificiallight in the additive color mixing is less with illumination of 300 lx.The deterioration of the image in the lower grayscale range due toartificial light can be improved by performing γ correction or grayscalecharacteristic correction in accordance with the brightness of theillumination.

[0179] The graph of FIG. 16 shows variations in color temperature whengray level is varied, where the illuminance is approximately 600 lx andthe γ value of the projected image is 2.0, 1.0, and 0.5, and the graphof FIG. 17 shows those variations when the illuminance is approximately300 lx and the γ value of the projected image is 2.0, 1.0, and 0.5. Inthis case, the set color temperature of the projector 20 itself is6500K.

[0180] As can be seen from FIGS. 16 and 17, the color temperaturestabilizes regardless of gray level variations when the γ value issmall, at illumination intensities of both 600 lx and 300 lx. It shouldbe noted, however, that the level of stabilization varies with thebrightness of the illumination.

[0181] This is at approximately 5500K (γ=0.5) under 600-lx illuminationwhereas it is approximately 6000K (γ=0.5) under 300-lx illumination.Note that the illumination used in these experiments was provided byfluorescent lamps. The color temperature of the artificial lightproduced by fluorescent lamps is a little more than 4000K, giving arather yellowish light.

[0182] The quantity of artificial light that is involved in the additivecolor mixing varies with the brightness of the artificial light. That isto say, different quantities of yellowish light (artificial light) areadded to the image, depending on the brightness of the artificial light.As a result, when an image is affected by illumination, it is consideredthat the level at which the color temperature of the projected imagestabilizes depends on the brightness of the artificial light, as shownin FIGS. 16 and 17.

[0183] This embodiment of the present invention makes it possible tomake the color temperature of the reproduced image settle at 6500K bysetting the color temperature of the projection light of the projector20 to higher than 6500K, when under the illumination of fluorescentlamps.

[0184] As can also be seen from FIGS. 16 and 17, the level at which thecolor temperature of the image moves changes with the brightness of theillumination, so that the setting of the color temperature of theprojection light (how far above the target color temperature to set it)depends on the brightness of the illumination.

[0185] With this embodiment of the present invention, the colortemperature of the image reproduced under illumination in each part ofthe grayscale can be stabilized and also the image can be reproduced atthe target color temperature, by using γ correction to cause the colortemperature of the image under illumination to stabilize at a certainlevel, then correcting the color temperature of the depicted image inaccordance with the brightness.

[0186] Description of Hardware

[0187] Note that the various means described below could be applied ashardware to be used in the previously described components.

[0188] For example, the input signal processing section 401 could beimplemented by using an A/D converter or the like, the color controlprocessing section 420 could be implemented by using RAM or a CPU or thelike, the output signal processing section 405 could be implemented byusing a D/A converter or the like, the L/V drive section 406 could beimplemented by using a liquid-crystal light bulb driver or the like, andthe calibration section 430 could be implemented by using an imageprocessing circuit or the like. Note that these components could beimplemented by hardware such as circuitry, or by software such asdrivers.

[0189] The functions of these components could also be implemented bythe reading of a program from an information storage medium 500. Meanssuch as a CD-ROM, DVD-ROM, ROM, RAM, or hard disk can be used as theinformation storage medium 500, and either a direct method or anindirect method could be used for reading that information.

[0190] Instead of the information storage medium 500, it is alsopossible to implement the above described functions by downloading aprogram for implementing those functions from a host device or the like,through a transfer path. In other words, information for implementingthe above described functions could be embodied over carrier waves.

[0191] The present invention has been described above by way of an idealembodiment thereof but the application of the present invention is notlimited to that embodiment.

[0192] Variations

[0193] If color compression and color expansion are not performed, byway of example, the function blocks can be simplified more than in FIG.3.

[0194] A functional block diagram of the image processing section withina projection in accordance with another example of this embodiment ofthe present invention is shown in FIG. 4.

[0195] This image processing section does not have the 3D-LUT storagesection 403, the color conversion section 408, the 3D-LUT storagesection 409, and the post-correction 3D-LUT storage section 414 of FIG.3, but instead a color temperature control section 470 is provided in acolor control processing section 422 and the target color temperaturemanagement section 472 is provided as part of the color temperaturecontrol section 470.

[0196] The color control processing update section 460 updates thetarget color temperature T from the target color temperature managementsection 472 to the target color temperature T′, based on environmentalinformation from the colored-light sensor 417, and outputs the targetcolor temperature T′ to the color temperature control section 470.

[0197] The color temperature control section 470 outputs to the outputsignal processing section 405 the colors of the image in such a manneras to achieve the target color temperature T′ from consideration of theambient light, as the corrected R3, G3, and B3 signals.

[0198] Note that a prior-art 1D-LUT is stored in the color temperaturecontrol section 470. In other words, the color correction is done with a1D-LUT so that there are none of the effects achieved by the colorcompression and color expansion due to the previously described 3D-LUT,but the use of the color temperature control function provided in theprior art has the effect of enabling color correction without theaddition of any new mechanism.

[0199] This makes it possible to configure a system that corrects forthe effects of the environment in a simple manner, by providing the new1D-LUT storage section 404 and managing a 1D-LUT for brightnesscorrection.

[0200] In addition, suitable color reproduction can be achieved becausethe color temperature T is corrected in accordance with the brightnessof the ambient light.

[0201] Note that the components of FIG. 3 are used for other functionsso further description thereof is omitted.

[0202] In addition, the LUTs stored in the previously described 3D-LUTstorage section 403 and 1D-LUT storage section 404 could provide valuesthat are scattered, such as in a mapping table form, or they couldprovide continuous values, such as those derived from functions, by wayof example.

[0203] Note that if values are in a dispersed form, such as in a mappingtable, substantially continuous values (corresponding colors) can beobtained by interpolation using a method such as Lagrange interpolationor linear interpolation.

[0204] In the embodiment of the present invention described above, thecolored-light sensor 417 was used as the visual environment detectionmeans by way of example, but an input means that inputs at least somepart of the environmental information (such as the presence/absence ofexternal light, the illumination type, or the screen type) or an imagedisplay means that displays an image for prompting the input of suchdetails could be used therefor. Both the colored-light sensor 417 and animage for inputting screen type could be used together.

[0205] With a screen, in particular, it is easy for people todistinguish the type of the screen easily, so it is possible to displayvarious types of screen for selection, by way of example, to enablereproduction of colors with reference to the screen type, with littlelikelihood of a human decision error.

[0206] In this case, the visual environment determined by the visualenvironment detection means applies to factors such as ambient light(such as artificial light or natural light) and the object on which theimage is displayed (such as a display, wall surface, or screen).

[0207] In particular, this embodiment of the present invention makes itpossible to apply more appropriate image correction by obtaininginformation on a component that is not much considered in the prior art(i.e., the screen), thus enabling the reproduction of more uniform imagecolors.

[0208] Note that the screen 10 described above is of a reflective type,but it could equally well be of a transparent type. If the screen is ofa transparent type, a sensor that scans the screen directly could beused as the colored-light sensor.

[0209] Similarly, the present invention can also be applied topresentations done by displaying images by a display means other than aprojection means such as the previously described projector. Other thana liquid-crystal projector, a projector using a digital micromirrordevice (DMD), a cathode ray tube (CRT), a plasma display panel (PDP), afield emission display (FED) device, an electro-luminescence (EL)device, or a direct-vision type of liquid crystal display device couldbe used as such a display means. Note that DMD is a trademark registeredto Texas Instruments Inc. of the USA.

[0210] It should be obvious that the present invention would also beeffective when displaying images in applications that are notpresentations, such as in meetings, for medical treatment, in the designor fashion world, in business activities, and in education, as well asfor general-purpose image displays such as movies, TV, video, and games.

[0211] If the input signals (R1, G1 and B1) are digital signals, the A/Dconverter section 440 is not necessary, and if the output signals (R6,G6 and B6) are digital signals, the D/A converter section 441 is notrequired. This is preferably done as necessary in accordance with theinput devices and output devices that are used.

[0212] Note that the functions of the previously described imageprocessing section of the projector 20 could be implemented by a simpleimage display device (such as the projector 20), or they could beimplemented by being distributed between a plurality of processingdevices (such as processing that is distributed between the projector 20and a PC).

[0213] In above embodiment, information in xyY (or Yxy) form is used ascolor information comprising brightness information, but it couldequally well be in another format such as Lab, Luv, or LCh.

[0214] The above described environmental information could also bevalues that express color and brightness in a form such as xyY, but itcould also be color and brightness correction amounts in a form such asΔxΔyΔY.

[0215] In addition, the embodiment described above related toapplication to a front-projection type of projector, but the presentinvention can equally well be applied to a rear-projection type ofprojector.

What is claimed is:
 1. An environment-compliant image display systemwhich corrects an image, based on environmental information thatexpresses visual environment in an area in which the image is displayed,and displays the image; the image display system comprising: correctionmeans which corrects input-output characteristic data for display thatis used by a means for displaying the image, the correction being insuch a manner as to increase an output value in at least a lowergrayscale range when the environment is affected by ambient light, basedon the environmental information.
 2. The image display system as definedin claim 1, wherein the correction means corrects the input-outputcharacteristic data by performing a predetermined calculation usingparameters that differ between a lower grayscale range and a grayscalerange other than the lower grayscale range.
 3. The image display systemas defined in claim 2, wherein the correction means corrects theinput-output characteristic data by performing a predeterminedcalculation based on a difference between a brightness value for actualenvironment which is comprised within the environmental information, anda brightness value for an ideal environment.
 4. The image display systemas defined in claim 3, wherein the correction means performs gammacorrection as at least part of the correction of the input-outputcharacteristic data.
 5. The image display system as defined in claim 4,wherein the correction means corrects color modification informationthat is stored in a predetermined storing region, in such a manner thata color temperature of the image to be displayed is adjusted, based on abrightness value for the actual environment that is comprised within theenvironmental information.
 6. The image display system as defined inclaim 5, wherein the color modification information is athree-dimensional look-up table.
 7. An environment-compliant imagedisplay system which corrects an image, based on environmentalinformation that expresses visual environment in an area in which theimage is displayed, and displays the image; the image display systemcomprising: a correction section which corrects input-outputcharacteristic data for display that is used by a means for displayingthe image, the correction being in such a manner as to increase anoutput value in at least a lower grayscale range when the environment isaffected by ambient light, based on the environmental information.
 8. Aprogram embodied on an information storage medium or in a carrier wave,the program for correcting an image, based on environmental informationthat expresses visual environment in an area in which the image isdisplayed, and displaying the image; the program implementing in acomputer: correction means for correcting input-output characteristicdata for display that is used by a means for displaying the image, thecorrection being in such a manner as to increase an output value in atleast a lower grayscale range when the environment is affected byambient light, based on the environmental information.
 9. The program asdefined in claim 8, wherein the correction means corrects theinput-output characteristic data by performing a predeterminedcalculation using parameters that differ between a lower grayscale rangeand a grayscale range other than the lower grayscale range.
 10. Theprogram as defined in claim 9, wherein the correction means corrects theinput-output characteristic data by performing a predeterminedcalculation based on a difference between a brightness value for actualenvironment which is comprised within the environmental information, anda brightness value for an ideal environment.
 11. The program as definedin claim 10, wherein the correction means performs gamma correction asat least part of the correction of the input-output characteristic data.12. The program as defined in claim 11, wherein the correction meanscorrects color modification information that is stored in apredetermined storing region, in such a manner that a color temperatureof the image to be displayed is adjusted, based on a brightness valuefor the actual environment that is comprised within the environmentalinformation.
 13. The program as defined in claim 12, wherein the colormodification information is a three-dimensional look-up table.